(1) A common authentication technique whereby an individual is prompted (the challenge) to provide some private information (the response). Most security systems that rely on smart cards are based on challenge-response. A user is given a code (the challenge) which he or she enters into the smart card. The smart card then displays a new code (the response) that the user can present to log in.

(2) In biometrics, challenge response is the term used to describe the method by which the identification of a person is detected based on voluntary or involuntary responses. Challenge response is a type of biometric system security.